In the related art, in scanners, copiers, multifunction peripherals (MFP), and other image forming apparatuses, an illuminating apparatus and a lens array having plural lenses arranged in the array are adopted to enable an image sensor to read an image on a document. In addition, in printers, copiers, multifunction peripherals (MFP), or other image forming apparatuses, an LED or other light emitting device and a lens array are adopted to enable imaging of light rays from the LED on a photoreceptor drum via the lens array so that an image is formed on the photoreceptor drum (exposure). Here, the lens array is formed as a combination of plural lenses and apertures.
However, for the lens array, if optical axes of the lenses that are both used for the passing of a light ray therethrough are offset from each other, the unevenness in the imaging characteristics and the light quantity degrades significantly. Also, when the plural lenses and the apertures are combined, the offset in the assembly operation leads to degradation in the performance of the imaging device and a rise in the manufacturing cost.
JP-A-2005-70519 proposed a scheme to avoid the degradation in the performance caused by the unevenness in the assembly of transparent devices to form a monolithic body. In this case, in an array having plural imaging devices each containing a lens surface and a roof mirror prism arranged in the array, a light shielding part is formed by a deep slit between the imaging devices. However, there is a problem of the depth of the light shielding part being deep and poor flow of resin during molding of the lens, etc., prolonging the forming time thereof.